/*
 * =============================================================
 *
 *        Project:  apue
 *
 *       Filename:  tellwait.c
 *
 *         Editor:  vim :set et ts=2 sts=2 sw=2
 *
 *         Author:  Martin Y. Yang , yang@libpix.org
 *
 *    Description:  
 *
 * =============================================================
 */

/**
 * @file
 * @brief Figure 10.24 Routines to allow a parent and child to synchronize
 */

#include "apue.h"

static volatile sig_atomic_t sigflag;           /* set nonzero by sig handler */
static sigset_t newmask, oldmask, zeromask;

static void sig_usr(int signo)                  /* one signal handler for SIGUSR1 and SIGUSR2 */
{
  sigflag = 1;
}

void TELL_WAIT(void)
{
  if (signal_lib(SIGUSR1, sig_usr) == SIG_ERR)
    err_sys("signal(SIGUSR1) error");
  if (signal_lib(SIGUSR2, sig_usr) == SIG_ERR)
    err_sys("signal(SIGUSR2) error");
  sigemptyset(&zeromask);
  sigemptyset(&newmask);
  sigaddset(&newmask, SIGUSR1);
  sigaddset(&newmask, SIGUSR2);

  /*
   * Block SIGUSR1 and SIGUSR2, and save current signal mask.
   */
  if (sigprocmask(SIG_BLOCK, &newmask, &oldmask) < 0)
    err_sys("SIG_BLOCK error");
}

void TELL_PARENT(pid_t pid)
{
  kill(pid, SIGUSR2);                           /* tell parent we're done */
}

void WAIT_PARENT(void)
{
  while (sigflag == 0)
    sigsuspend(&zeromask);                      /* and wait for parent */
  sigflag = 0;
  /*
   * Reset signal mask to original value.
   */
  if (sigprocmask(SIG_SETMASK, &oldmask, NULL) < 0)
    err_sys("SIG_SETMASK error");
}

void TELL_CHILD(pid_t pid)
{
  kill(pid, SIGUSR1);                           /* tell child we're done */
}

void WAIT_CHILD(void)
{
  while (sigflag == 0)
    sigsuspend(&zeromask);                      /* and wait for child */
  sigflag = 0;
  /*
   * Reset signal mask to original value.
   */
  if (sigprocmask(SIG_SETMASK, &oldmask, NULL) < 0)
      err_sys("SIG_SETMASK error");
}

